#include "kernel.h"


/* 
 * 
 * Defines an IDT entry 
 *
 */
struct idt_entry
{
    unsigned short base_lo;
    unsigned short sel;
    unsigned char always0;
    unsigned char flags;
    unsigned short base_hi;
} __attribute__((packed));


struct idt_ptr
{
    unsigned short limit;
    unsigned int base;
} __attribute__((packed));

/* 
 * Declare an IDT of 256 entries. Although we will only use the
 *  first 32 entries in this tutorial, the rest exists as a bit
 *  of a trap. If any undefined IDT entry is hit, it normally
 *  will cause an "Unhandled Interrupt" exception. Any descriptor
 *  for which the 'presence' bit is cleared (0) will generate an
 *  "Unhandled Interrupt" exception 
 *
 * NOTE: IDT holds 32 bit addresses which are split to high and low 
 *  each of 16 bits (they are called base_hi and base_lo in the above structure)
 *
 */
struct idt_entry idt[256];
struct idt_ptr idtp;

/* 
 * 
 * This exists in 'start.asm', and is used to load our IDT 
 *
 */
extern void idt_load();

/* 
 *
 * Use this function to set an entry in the IDT. Alot simpler
 *  than twiddling with the GDT ;) 
 *
 */
void idt_set_gate(unsigned char num, unsigned long base, unsigned short sel, unsigned char flags)
{
    /*
     * 
     * The interrupt routine's base address 
     *
     */
    idt[num].base_lo = (base & 0xFFFF);
    idt[num].base_hi = (base >> 16) & 0xFFFF;

    /*
     *
     * The segment or 'selector' that this IDT entry will use
     *  is set here, along with any access flags 
     *
     */
    idt[num].sel = sel;
    idt[num].always0 = 0;
    idt[num].flags = flags;
}

/* 
 *
 * Installs the IDT 
 *
 */
void idt_install()
{
    /*
     *
     * Sets the special IDT pointer up, just like in 'gdt.c' 
     *
     */
    idtp.limit = (sizeof (struct idt_entry) * 256) - 1;
    idtp.base = (unsigned int) &idt;

    print((unsigned char *) "IDT...");
    /*
     *
     * Clear out the entire IDT, initializing it to zeros 
     *
     */
    memset(&idt, 0, sizeof(struct idt_entry) * 256);

    /*
     *
     * Add any new ISRs to the IDT here using idt_set_gate 
     *
     */



    /*
     *
     * Points the processor's internal register to the new IDT
     *
     */
    idt_load();
}
